Process for converting coarse aqueous polymer emulsion to fine emulsion

ABSTRACT

The preparation of stable aqueous latices from solvent dispersions of elastomers and other high polymer compositions has presented problems including excessive viscosity during processing and foaming, which have produced losses and increased costs. Herein combinations of steps are disclosed which reduce or eliminate various of these problems and enable the preparation of stable latices of high solids content. The process in common with that of related copending applications is characterized, inter alia, by the establishment of a flow of steam as a continuous phase into which an emulsion of a cement of the polymer is dispersed as an aerosol of latex droplets in a solvent-vapor continuum, followed by coalescence of the latex droplets and separation of the resulting coalesced liquid phase from the resulting solvent-vapor phase. In one embodiment of the present method an aqueous emulsion is prepared the dispersed phase of which principally comprises particles of precursor latex particle size and which may contain a lesser proportion of particles of greater than precursor latex particle size. This emulsion is converted to a stable latex by subjecting the same to special conditions which cause selective agglomeration of the particles of greater than precursor latex particle size, and removing the so agglomerated particles to yield a latex essentially free of particles of greater than colloidal size. In preferred embodiments provision is made for the continuous production of aqueous emulsion of polymer solvent cement essentially entirely of precursor latex particle size, which may be of narrow size distribution, or may have imparted thereto a wider size distribution, or an altered particle size or viscosity or both. As in the processes of my prior applications hereinafter referred to, the separation of the gaseous and liquid latex phases is effected by impinging the same on a liquid body, preferably a flow of partially concentrated liquid latex; and preferred arrangements for generating the aerosol, for effecting the said impingement, for effecting concentration of the latex under controlled conditions minimizing the formation of coagulum therefrom, and for recovering the latex from the gaseous phases, are also disclosed, which may be employed in lieu of or together with other features of said copending applications. In certain embodiments, in addition, special provisions are made for eliminating, from the latex, particles of greater than colloidal size by controlling the heating and stripping operations so that in combination, such larger particles are essentially avoided and/or agglomerated or coagulated and removed to yield latex essentially free of greater than colloidal sized particles. In other embodiments special provisions are made for altering the viscosity of the aqueous polymer/solvent emulsion and/or of the latex product, by special treatment of at least a part thereof before delivery from the system. Furthermore, special provisions are made for cOagulum removal and recovery, and to contribute to a more expeditious processing of the materials into stable latices and a reduction in coagulum losses and increase in efficiency.

United States Patent Burke, Jr.

[451 Jan. 21, 1975 PROCESS FOR CONVERTING COARSE AQUEOUS POLYMER EMULSION TO FINE EMULSION Oliver W. Burke, Jr., PO. Box 2266, Fort Lauderdale, Fla. 33061 22 Filed: Jan. 15, 1973 [21] Appl. No.: 323,381

Related US. Application Data [63] Continuation-impart of Ser. No. 226,419, Feb. 15, 1972, which is a continuation-impart of Ser. No. 817,494, April 18, 1969, abandoned, and a continuation-in-part of Ser. Nos. 621,997, March 7, 1967, Pat. No. 3,503,917, and Ser. No. 691,823, Dec. 19, 1967, Pat. No. 3,652,482, and Ser. No. 767,790, Oct. 15, 1968, Pat. No. 3,644,263, and Ser. No. 784,596, Dec. 18, 1968, Pat. No. 3,622,127.

[76] Inventor:

52 us. c1... 2 0 29 204/ 1 59.22, 260/296 XA. 260/296 DT, 260/296 PM, 260/297 R,

260/297 T, 260/297 EM, 260/297 PT, 260/815 [51] Int. Cl. C08t 45/24 58 1 Field ofSearch...260/29.6 R, 29.6 XA, 29.6 PT, 260/296 PM, 29.7 R, 29.7 EM, 29.7 PT,

Primary Examiner-Harold D. Anderson Attorney, Agent, or Firm-Hall & Houghton ABSTRACT The preparation of stable aqueous latices from solvent dispersions of elastomers and other high polymer compositions has presented problems including excessive viscosity during processing and foaming, which have produced losses and increased costs. Herein combinations of steps are disclosed which reduce or eliminate various of these problems and enable the preparation of stable latices of high solids content. The process in common with that of related copending applications is characterized, inter alia, by the establishment of a flow of steam as a continuous phase into which an emulsion of a cement of the polymer is dispersed as an aerosol of latex droplets in a solvent-vapor continuum,

followed by coalescence of the latex droplets and separation of the resulting coalesced liquid phase from the resulting solvent-vapor phase. In one embodiment of the present method an aqueous emulsion is pre pared the dispersed phase of which principally comprises particles of precursor latex particle size and which may contain a lesser proportion of particles of greater than precursor latex particle size. This emulsion is converted to a stable latex by subjecting the same to special conditions which cause selective agglomeration of the particles of greater than precursor latex particle size, and removing the so agglomerated particles to yield a latex essentially free of particles of greater than colloidal size.

In preferred embodiments provision is made for the continuous production of aqueous emulsion of polymer solvent cement essentially entirely of precursor latex particle size, which may be of narrow size distribution, or may have imparted thereto a wider size distribution, or an altered particle size or viscosity or both.

As in the processes of my prior applications hereinafter referred to, the separation of the gaseous and liquid latex phases is effected by impinging the same on a liquid body, preferably a flow of partially concentrated liquid latex; and preferred arrangements for generaating the aerosol, for effecting the said impingement, for effecting concentration of the latex under controlled conditions minimizing the formation of coagulum therefrom, and for recovering the latex from the gaseous phases, are also disclosed, which may be employed in lieu of or together with other features of said copending applications.

In certain embodiments, in addition, special provisions are made for eliminating, from the latex, particles of greater than colloidal size by controlling the heating and stripping operations so that in combination, such larger particles are essentially avoided and/or agglomerated or coagulated and removed to yield latex essentially free of greater than colloidal sized particles.

In other embodiments special provisions are made for altering the viscosity of the aqueous polymer/solvent emulsion and/or of the latex product, by special treatment of at least a part thereof before delivery from the system.

Furthermore, special provisions are made for coagulum removal and recovery, and to contribute to a more expeditious processing of the materials into stable latices and a reduction in coagulum losses and increase in efficiency.

19 Claims, 26 Drawing Figures PAYENTEBJMI ms 3,862,078

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E s z 8x 5 WK E Ev .3 & 9 N w 6* mm mps U PATENIEI] JANZI I975 Wm USUF 16 52w iD =EMu| s|oN 2C 550v" c CREAMING V AID seo sel 562 CREAMING H4 564 L AID PUMP AND E v MIXER v v HIGH PRESSURE COOLER HDMDGEMZER HEATER PUMP AND 566 v VIBRATING REED HOMOGENIZER v 563 M V V LATEX z u L 260) 24m. 23w 24|3L M|XER FREEZE a mm 1 v 2e: LATEX c 262 264 CR A MING 265 PUMP AND M|XER HIGH PRESSURE COOLER L- HOMOGENIZER HEATER PUMP AND 266 VIBRAT|NG REED HOMOGENIZER PATENTED JAN? 1 5 SHEH USOF 16 PATENTEB JAN 2] I975 SREEI 100! 16 Riv SHEET 1311F16 PATENTED JANZ I [975 PATENTED 3, 862 O78 SHEET 1B OF 16 whxxm PROCESS FOR CONVERTING COARSE AQUEOUS POLYMER EMULSION TO FINE EMULSION CROSS REFERENCE TO RELATED APPLICATIONS This is a continuation-in-part of my application Ser. No. 226,419, filed Feb. 15, 1972 as a continuation-inpart of my application Ser. No. 817,494 filed Apr. 18, 1969 (now abandoned), an improvement over and continuation-in-part of my applications Ser. No. 621,997, filed Mar. 7, 1967 (U.S. Pat. No. 3,503,917 issued Mar. 31,1970), Ser. No. 69l,823, filed Dec. 19, 1967 (U.S. Pat. No. 3,652,482 issued Mar. 28, 1972), Ser. No. 767.790, filed Oct. 15, 1968 (U.S. Pat. No. 3,644,263 issued Feb. 22, 1972), and Ser. No. 784,596, filed Dec. 18, 1968 (U.S. Pat. No. 3,622,127 issued Nov. 23, 1971 the disclosures of which are herein incorporated by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention like those of my aforesaid copending applications relates to the production of high solids content aqueous latices with reduced losses, from solvent dispersions of cements of polymer compositions, and aims generally to provide improved method and apparatus combinations therefor, and new products produced thereby.

2. Description of the Prior Art To date, in the practical art, synthetic latices of high polymers have been primarily prepared by emulsion polymerization, which can produce latices of uniform colloidal particle size. In contrast, it is difficult to prepare latices from the class of high polymers made by essentially anhydrous catalyst polymerizations. In this latter case it has been proposed to prepare aqueous latices of high polymers from solvent solutions thereof by processes of the type which comprise the general steps of 1) providing a dispersion or cement of the polymer in a volatile organic solvent for the polymer, 2) adding to such dispersion water and an aqueous emulsifier therefor and emulsifying the same to produce an emulsion, (3) stripping the volatile organic solvent from the said emulsion, and (4) recovering the resulting latex product. However, in the practical art difficulty has been experienced in attempting to render such proposed processes commercially feasible, inter alia, in that l aqueous emulsification and stripping of solvent dispersions or cements of the high polymer materials, especially when dilute, have yielded latices of only medium solids and high emulsifier content which render them commercially impractical; (2) in that the emulsions have tended to foam excessively during stripping; and (3) in that the emulsions have tended to form coagulum by coalescence of the polymer phase as well as by drying out especially on contact with heated surfaces, during the stripping and/or concentrating processes, and (4) in that such processes have tended to yield latices of poor mechanical stability, i.e. latices which when subjected to mechanical shear during blending with other materials in the industrial applications thereof, are apt to undergo coagulation thereby rendering the blended materials unsuitable for their intended latex applications especially when the emulsifier content is low.

SUMMARY OF THE INVENTION The particular improvements hereinn disclosed and claimed may be employed in practicing any of the sev eral earlier embodiments of process and apparatus set forth in my aforesaid applications.

In such earlier embodiments, while the emulsification and homogenization under ideal conditions can produce an aqueous emulsion having substantially all of its dispersed particles of precursor latex particle size; con siderations of economy, storage, or other factors, may result intentionally or unintentionally in the production of a fine emulsion that, while principally comprising dispersed particles of precursor latex particle size which on removal of solvent therefrom yield latex particles in the colloidal size range, may contain a smaller proportion of particles of greater than precursor latex particle size. Such particles when relieved or their solvent and included in the latex product, do not appear to have much effect on the shelf life or storage stability of the latex, but do seem to act as initiators of coagulation when the latices containing them are subjected to mechanical working.

Accordingly, it is highly desireable that latices for uses in which they will be subjected to mechanical working be essentially free of such noncolloidal sized particles, and that such essential freedom be evidenced by the ability of the latex to pass a standardized mechanical stability test. Any of several such standardized tests may be employed, but the test preferred and referred to in the present specification is made as follows:

a. A 50 gram sample of 20 percent solids latex is placed in a 300 ml tall form beaker (Pyrex No. 1040) and agitated for 30 minutes with a Hamilton Beach mixer (Model No. 930).

b. The so agitated latex is then poured through a 200 mesh stainless steel screen and any retained coagulum is washed with water, dried at C. and weighed.

c. A mechanically stable latex should yield by this test less than 5 percent of its solid content as coagulum, and preferably essentially no coagulum.

The improvements of the present invention provide methods and means facilitating the production of such mechanically stable latices, including inter alia, severally and interdependently (l) the provision of an improved continuous emulsification system for more readily attaining desired or ideal conditions, or a close approximation thereof, e.g. for producing an aqueous emulsion of polymer-solvent cement essentially free of cement droplets of greater than precursor latex particle size; (2) the provision ofa method and means for insuring the production of such mechanically stable latices from aqueous emulsions of solvent polymer cements notwithstanding less than ideal preparation of the initial aqueous emulsion of solvent/polymer cement, by a treatment which differentiates the susceptibility of the colloidal sized and non-colloidal sized resulting particles to heat, and then applies heat and mechanical treatment thereto in a manner to selectively coagulate the particles of greater than colloidal size without undue coagulation of the colloidal sized particles, so that the latex will be essentially free of particles detrimental to its mechanical stability, and preferably with recovery and reuse of the so selectively agglomerated and removed polymer coagulum; (3) the adaptation of the second improvement, just discussed, for treating latices prepared from emulsions of solvent/polymer cements and having poor mechanical stability. to improve the mechanical stability thereof as measured by the aforesaid test; (4) the provision of apparatus for facilitating the practice of the aforesaid and other process improvements.

in a first embodiment of the invention the formation of a latex from an organic solvent dispersion of a composition of an organic solvent soluble or dispersible polymer is effected by a process of the type which comprises:

1. providing a dispersion of the polymer composition, preferably one having a dry solids content within the range of 8 to 50 percent by weight, in an essentially waterimmiscible volatile solvent which itself or as azeotrope with water has a boiling point lower than that of water at atmospheric pressure,

adding water and emulsifier to said dispersion in proportions to form an emulsion having water as its continuum and emulsifying the same so that the discontinuous phase thereof is in particles at least principally of precursor latex particle size, such proportions preferably being in the range of 0.4 to percent emulsifier by weight based on the poly mer, and 0.4 to 2.5 parts by volume of water per part of cement, and the emulsiftcation preferably being effected continuously by a novel subcombination which can minimize recycle, or provide controlled recycle. as hereinafter set forth;

3. stripping the solvent from the emulsion to form a latex, and

4. recovering the latex product, preferably after concentration thereof,

and which comprises the further steps of:

5. providing a moving flow of gas comprising steam as an initial continuous phase,

dispersing the said emulsion into the flow of steam as the initial continuous phase while subjecting the phases to a decrease of pressure and maintaining the temperature thereof below the limiting temper' ature for stability of the emulsion of particles of precursor latex particle size, thereby vaporizing solvent from the dispersed droplets and forming latex and vapor, this step preferably being conducted in a manner to maintain the said temperature in the upper portions of the range for stability of the emulsion and to avoid explosive release of the solvent from the aerosol particles while avoiding impact against solid surfaces at velocities apt to produce coagulum, as hereinafter set forth, and in this embodiment mechanical stability of the latex may be further be assured by the combination in the process of the further steps of:

7. subjecting the latex prepared by step 6 to an increase in temperature for a period of time only sufficient to destabilize, and permit coagulation and- /or agglomeration from the latex of, particles of greater than colloidal size that may be present therein without such time period being sufficiently long to substantially effect coagulation and/or agglomeration of the latex particles of colloidal size, and

8. separating from the latex any coagulum formed,

and 9 the concentration of the latex, referred to in step (4), preferably being effected by heating without vaporization followed by vaporization in the absence of heating, as hereinafter described.

In particular species of this first embodiment: step (7) may be practiced by passing the latex formed in step (6) in contact with a surface heated in the range of 2] 2 to 260F., preferably 225 to 245F., for a sufficient time to effect the destabilization and coagulation of such particles of greater than colloidal size, (by the term coagulation" is meant the enlargment of such particles to separable size by agglomeration with non colloidal and/or colloidal sized latex particles with the aid of surfaces heated to the temperature range 212F. to 260F.), and this practice may be carried out in the presence or absence of solvent vapor produced in step (6). And in the several species of this first embodiment, the process preferably further includes the step of recycling the coagulum separated in step (8) to form part of the material employed in forming the emulsion in step (2), and preferably in this step the coagulated polymer is dissolved in solvent the same as that used in step (l) and the resulting solution is employed to form a part of the solvent dispersion of polymer composition produced in step l Also, in the several species of this first embodiment step (4) is preferably practiced by establishing a separating zone maintained at subatmospheric pressure, establishing a flow of latex through said separating zone, introducing into said sep' arating zone the latex droplets and vapor produced by step (6) and impinging said droplets upon the flow of latex therein, withdrawing vapor from said separating zone, and withdrawing the combined latices from said separating zone, with or without other cooperating steps hereinafter disclosed, or disclosed in the aforesaid applications, e.g., when a very fine latex is being pro duced, and being altered in particle size by grafting as in 27 of FIG. 1 herein (or by treatments exemplified in FIGS. 7, 7A and 7B, hereinafter described).

And in addition to the above process improvements the invention provides new apparatus combinations permitting continuous operation of the above pro cesses, or of processes disclosed in the aforesaid copending applications,

Thus, objects of the invention, severally and interdependently, are to provide new apparatus features and new combinations of steps, which contribute to produce an improved process and which enable the production of improved latices. Other objects and advantages of the invention will be apparent from the above general description and the following more particular descriptions of preferred embodiments thereof, which, however, are illustrative but not restrictive of the in vention, the scope of which is more particularly pointd out in the appended claims.

By the term latex" as used herein is meant an aque ous dispersion of line particles of polymer composition and emulsifier material which latex may be of the noncreaming or creaming type depending on its intended use, the non-creaming types having essentially all of their suspended particles in the colloidal size range characterized by Brownian movement, i.e., in the size range of latices having good mechanical stability; and the polymer thereof may be selected, e.g., from the following types and combinations thereof:

i. homopolymer,

ii. interpolymer including block and graft polymer,

iii. hydrocarbon polymer,

iv. polar polymer.

v. polymer composition comprising polymer material selected from (i) through (iv) above and compounding ingredients including reinforcing fillers and/or non-reinforcing fillers.

By the term "colloidal particle" or colloid" as used herein is meant particles in the size range of 500 A to l0,000 A diameter, and by the term upper portion of the colloidal size range is meant particles in the size range of above 2,000 A, preferably 3,000 to 5,000 A, diameter.

By the term precursor latex particle size" is meant a particle of polymer composition and solvent of such a size that when relieved of its solvent content the resulting particle is a colloidal particle as above defined.

By the term greater than precursor latex particle size" is meant a particle of polymer composition and solvent which, when relieved of its solvent yields particles of greater than colloidal size, which reduce the mechanical stability of the latex. Such particles are usually from to 1,000 times as large as particles of precursor latex particle size.

By the term resin" as used herein is meant those inflammable amorphous vegetable products of secretion or disintegration usually formed in special cavities of plants and such resins are generally insoluble in water and soluble in alcohol, fusible and of concoidal fracture and are usually oxidation or polymerization products of terpenes and the like.

By the term synthetic resin" as used herein is meant organic oxidation, polymerization or condensation products not produced in nature but produced synthetically and having resin-like properties and which term does not include the synthetic rubbers. Synthetic resins include (I) the resinous polymers produced from unsaturated petroleum compounds by oxidation and/or polymerization such as resinous alpha-olefin polymers, (2), condensation resins such as the phenolic resins, the aminoplast resins, alkyd resins, glycerol-phthalate resins and the like; (3) the non-rubber-like resinous polymers produced by cyclizing, hydrogenating or halogenating unsaturated rubbery polymers such as cyclized polyisoprene, chlorinated polyisoprene and the like, (4) resins derived from coal tar chemicals such as the cumaron-indene resins; (5) resinous materials prepared from vinyl, vinylidene and vinylene monomers; (6) resinous copolymers prepared from vinyl, vinylidene and vinylene monomers with conjugated diene monomers such as the high styrene-butadiene resins (7) resinous copolymers prepared from vinyl, vinylidene, and vinylene monomers including alpha-olefins such as the ethylene-vinyl acetate copolymers. As used herein the term synthetic resins" is restricted to those synthetic resins which are soluble or dispersable in at least one solvent which is essentially water immiscible and which itself or as its azeotrope with water has a boiling point lower than that of water at atmospheric pressure.

By the term polymer composition" is meant elastomers and other high polymers (molecular weights I0 to l0) and/or lower polymers ($004,000 molecular weight) and said term polymer composition encompasses polymer materials, grafted or ungrafted including the synthetic resins, natural resins, natural rubber and the synthetic rubbers, synthetic plastic materials, asphalts and asphaltenes of natural and synthetic origin and such polymers with and without copounding ingredients and combinations of the foregoing.

The terms solvent/polymer composition" or "solvent/polymer cement" refer to polymer composition which has been dispersed or dissolved in at least one solvent which is essentially water immiscible and which itself, or as its azeotrope with water has a boiling point lower than that of water at atmospheric pressure.

in practicing the present invention conditions are created combinations of which render practical the production of aqueous latices from solvent dispersions of high polymer compositions. These conditions, inter alia, include, severally and in cooperating combinations:

1. The use of particular solvents for the polymers which are essentially immiscible with water in liquid phase, and which have boiling points less than the boiling point of water at atmospheric pressure, or which form azeotropes with water which have boiling points less than the boiling point of water at atmospheric pressure. The solvents, for example, include the C to C acyclic hydrocarbon solvents, cyclehexane and methylcyclohexane, the C to C aromatic hydrocarbon solvents, and the less desirable halo-substituted C to C5 hydrocarbon solvents when required and combinations of two or more members of the foregoing groups. Preferred are such solvents which have boiling points higher than that of water but which form azeotropes with water that have boiling points lower than that of water, which preferred group comprises especially the aromatic solvents including toluene, the xylenes, ethyl benzene, cumene, etc.

2. The formation of relatively high solids cements of the polymer composition and the solvent therefor selected as aforesaid, which cements preferably have viscosities of over 1,000 centipoises and more preferably over 7,000 to 10,000 centipoises, and even over l0,000 to 20,000 centipoises, which high viscosities can be tolerated because of other cooperating steps of the process. The cements of emulsifiable viscosities in the preferred range of 7,000 to 10,000 centipoises generally comprise by weight at least 25 percent and preferably over 50 percent of solvent, depending on the polymer to which the invention is applied.

The Polymer Material (1) (See FIG. 1)

The new process is applicable to the preparation of latices from solvent solutions or dispersions of polymer materials which are essentially solvent soluble or dispersable and essentially water insoluble, including natural rubber and polymers of ethylenically unsaturated monomer material containing from 2 to 20 carbon atoms, preferably from 2 to l0 carbon atoms. it is especially applicable to those elastomers and plastomers which, with or without plasticiser, have the foregoing properties and properties adapting their latices for use as adhesives, binders, film forming materials, coating materials, etc. Examples of such elastomers and plastome'rs, illustrative but not restrictive of those to which the invention can be applied, are as follows: butyl rubber, chlorinated butyl rubber, polyisobutylene, polybutadiene, polyisoprene, polyethylene, polypropylene (including both amorphous and/or crystalline polypropylene), ethylene-propylene polymer, ethylenepropylene-diene terpolymer, ethylene-vinylidene monomer interpolymers (including ethylene-vinyl acetate copolymers), butadiene-ethylene copolymers, propylene-butene-l copolymers, butadiene-styrene copolymer, nitrile rubbers (including butadieneacrylonitrile and butadiene-methacrylonitrile copolymers), natural rubber, hydrocarbon resins, any of the foregoing polymers grafted with polar or other polymer 

2. Process as claimed in claim 1, which further comprises: d. impinging the flow passing through at least one of said homogenizing unit orifices as maintained in step (c) against the free tip of a vibrating reed before it leaves the outlet chamber of said homogenizing unit.
 3. Process as claimed in claim 2, in which said step (d) is effected in the most downstream of said homogenizing units.
 4. Process as claimed in claim 2, in which said step (d) is effected in a plurality of said homogenizing units.
 5. Process as claimed in claim 2, in which said step (d) is effected in each of said homogenizing units.
 6. Process as claimed in claim 1, in which the pressure raising means of the several homogenizing units are operated to produce high pressures in at least two of said units differing by at least 50 psig.
 7. Process as claimed in claim 1, in which the pressure raising means of the successive homogenizing units are operated to produce high pressures increasing from unit to unit in the downstream direction by at least 50 psig.
 8. Process as claimed in claim 1, in which a portion of the flow of emulsion passing through the restricted orifice of one of said homogenizing units is continuously recycled to broaden the size distribution of the precursor latex size particles of the converted emulsion.
 9. Process as claimed in claim 1, in which a portion of the flow of emulsion passing through the restricted orifice of one of said homogenizing units is continuously recycled within the unit to broaden the size distribution of the precursor latex size particles of the converted emulsion.
 10. Process as claimed in claim 1, in which any recycle of the flow through the restricted orifices of said units is essentially minimized so as to maintain a narrow size distribution of the precursor latex size particles in the converted emulsion.
 11. Process as claimed in claim 1, in which the flow discharged from the most downstream of said units is split and recombined after the particle size of one portion thereof is altered by passing it through a separate homogenizer.
 12. Process as claimed in claim 1, in which the emulsion removed from the flow to one unit in step (c) is recycled to a point upstream of the next preceding unit.
 13. Process as claimed in claim 1, in which the emulsion removed from the flow to one unit in step (c) is recycled to a point upstream of the most upstream of said units.
 14. Process including the steps of claim 1, which further comprises d. conveying the emulsion from the most downstream of said units to a point of delivery, and e. treating at least a portion of the emulsion being conveyed in step (d) to reduce its viscosity.
 15. Process as claimed in claim 14, wherein in step (e) the emulsion is subjected to treatment to enlarge the average particle size thereof.
 16. Process as claimed in claim 14, wherein in step (e) the emulsion is treated to reduce the quantity of emulsifier in its aqueous phase.
 17. Process as claimed in claim 15, wherein in step (e) the emulsion is treated to reduce the quantity of emulsifier in its aqueous phase.
 18. Process as claimed in claim 1, wherein the fine emulsion added to the flow in step (c) (1) is emulsion which has been discharged from the most downstream of said units.
 19. Process as claimed in claim 14, wherein the fine emulsion added to the flow in step (c) (1) is emulsion which has been conveyed through step (d). 